1. Field of the Invention
The present invention relates to a heating apparatus, and more particularly, to a heating apparatus having a burner and a heat exchanger which are coupled to each other.
2. Description of the Prior Art
Heating apparatuses which have a burner and a heat exchanger coupled to each other are well known in the art. For example, Japanese Patent Application Publication No. 7-103413 discloses such a conventional heating apparatus.
FIG. 1 illustrates the above-mentioned conventional heating apparatus 100. In FIG. 1, for purposes of explanation only, the left side of the figure will be referenced as the forward end or front of heating apparatus 100, and the right side of the figure will be referenced as the rearward end or rear of heating apparatus 100.
With reference to FIG. 1, the conventional heating apparatus 100 includes a burner 200' and heat exchanger 50. Burner 200' comprises a burning mechanism 220, a fan motor 30 associated with the burning mechanism 220, and cylindrical casing 210' housing the burning mechanism 220 and the fan motor 30 therein. Cylindrical casing 210' comprises a separate first casing portion 211 and second casing portion 212 to the rear of first casing portion 211. First and second casing portions 211 and 212 respectively house fan motor 30 and burning mechanism 220.
First and second casing portions 211 and 212 are joined to each other at their rear end and front ends, respectively, in a fashion of faucet joint. Casing portions 211 and 212 are firmly and releasably connected to each other by, for example, a plurality of screws 240 through a corresponding pair of L-shaped plates 241 and 242 which respectively are fixedly connected to a rear end region of first casing portion 211 and a front end region of second casing portion 212. When the first and second casing portions 211 and 212 are connected to each other, they are arranged such that their longitudinal axes are aligned with each other. Furthermore, circular openings 241a and 242a having female screw threads are formed in L-shaped plates 241 and 242 for receiving a shaft portion of screws 240 having a male screw thread.
First cylindrical member 21 is disposed in a front section of an inner hollow space of second casing portion 212. First cylindrical member 21 comprises a large diameter region 21a, a small diameter region 21b to the rear of large diameter region 21a, first annular planar region 21c which connects large diameter region 21a to small diameter region 21b, and second annular planar region 21d which extends radially inwardly from an inner periphery of a rear end of small diameter region 21b. An inner terminal end of second annular planar region 21d is located at a position which is about one-third of a diameter of small diameter region 21b, so that circular opening 21e is centrally defined within second annular planar region 21d of first cylindrical member 21. An outer diameter of large diameter region 21a is designed to be about equal to an inner diameter of second casing portion 212. First and second annular planar regions 21c and 21d are arranged to be parallel to a plane perpendicular to the longitudinal axis of first cylindrical member 21. As illustrated in FIG. 2, a plurality of indents 21f are formed at second annular planar region 21d of first cylindrical member 21 so as to receive a head portion of the corresponding later-mentioned flush screws 22.
Second cylindrical member 23 is disposed within the circular opening 21e of first cylindrical member 21. Second cylindrical member 23 includes a flange portion 23a which extends radially outwardly from a periphery of a front end of second cylindrical member 23. As illustrated in FIG. 2, a front end section of indents 21f are received in the corresponding circular holes 23b which are formed at the flange portion 23a of second cylindrical member 23, so that flange portion 23a of second cylindrical member 23 is disposed on a front end surface of second annular planar region 21d of first cylindrical member 21.
With reference to FIG. 2 in addition to FIG. 1, fan motor 30 is disposed within first casing portion 211 at a position which is in front of first cylindrical member 21. Fan motor 30 is fixedly secured to second annular planar region 21d of first cylindrical member 21 at its rear end by, for example, a plurality of flush screws 22. A shaft portion of flush screw 22 penetrates through a hole 21g which is formed at a bottom end of indent 21f, and the head portion of flush screw 22 is received within indent 21f. The shaft portion of flush screws 22 further penetrate through the corresponding collars 24 which are disposed between a housing 31 of fan motor 30 and the flange portion 23a of second cylindrical member 23. Each collar 24 includes a truncated cone portion 24a formed at its rear end. The truncated cone portion 24a of each collar 24 faces a rear end surface of the flange portion 23a of second cylindrical member 23.
A front end section of the shaft portion of each flush screw 22 is screwed into the housing 31 of fan motor 30, so that each collar 24 is firmly disposed between the housing 31 of fan motor 30 and the flange portion 23a of second cylindrical member 23. As a result, fan motor 30 is firmly secured to the second annular planar region 21d of first cylindrical member 21 through collars 24 and flange portion 23a of second cylindrical member 23.
Front and rear ends of drive shaft 32 of fan motor 30 respectively extend forwardly and rearwardly from the housing 31 of fan motor 30. First fan 33 is firmly secured to a front end portion of drive shaft 32 by means of an appropriate securing manner, so that first fan 33 rotates together with the drive shaft 32 during operation of the heating apparatus 100. Second fan 34 is firmly secured to the rear end of drive shaft 31 by, for example, bolt 34a, so that second fan 34 also rotates together with the drive shaft 32 during operation of the heating apparatus 100.
Cup-shaped member 25 is firmly mounted about the rear end portion of drive shaft 32 at a position between the second fan 34 and a rear end of the second cylindrical member 23. Accordingly, cup-shaped member 25 rotates together with the drive shaft 32 during operation of the heating apparatus 100. An annular side wall 25a of cup-shaped member 25 surrounds a rear end portion of second cylindrical member 23 with creating a radial air gap therebetween. Furthermore, cup-shaped member 25 is slightly broadened forwardly.
Fuel supply pipe 26 is disposed within casing 210', and is arranged to generally extend along first and second cylindrical members 21 and 23. As illustrated in FIG. 2, one end of fuel supply pipe 26 slightly projects from the rear end of second cylindrical member 23, but is located at a position forward of a bottom end 25b of cup-shaped member 25. The one end of fuel supply pipe 26 is bent in generally a right angle to form an nozzle 26a. Nozzle 26a of fuel supply pipe 26 is arranged to be situated in a zone which is defined below.
With reference to FIG. 3, on a plane perpendicular to the longitudinal axis of drive shaft 32 of fan motor 30, axes "Y" and "X" are defined as follows. Axis "Y" is located on a first line which connects the longitudinal axis of drive shaft 32 of fan motor 30 and a center of a base of nozzle 26a. Axis "X" is located on a second line which intersects with axis "Y" at the center of the base of nozzle 26a at a right angle. Upon a definition of axes "X" and "Y", nozzle 26a is arranged such that the longitudinal axis of nozzle 26a is situated in a first quadrant of axes "X" and "Y" while the rotational direction of drive shaft 32 of fan motor 30 is clockwise as indicated by arrow "A". Preferably, nozzle 26a is arranged, such that an angle created between the longitudinal axis of nozzle 26a and axis "Y" is 30.degree..
Fuel supply pipe 26 is radially spaced from drive shaft 32 of fan motor 30 and the side wall 25a of cup-shaped member 25 so that interference between the fuel supply pipe 26, and the drive shaft 32 of fan motor 30 and the cup-shaped member 25 is prevented during rotation of the drive shaft 32 of fan motor 30. As illustrated in FIG. 2, fuel supply pipe 26 is secured to a front end surface of flange portion 23a of second cylindrical member 23 by, for example, caulking, so that caulked portion 23c is formed at the front end surface of flange portion 23a. The other end of fuel supply pipe 26 is fixedly connected to coupling element 26b which is used for connecting the fuel supply pipe 26 to an external fuel supply pipe (not shown) which is connected to a fuel tank (not shown). As illustrated in FIG. 4, the coupling element 26b is received in semicircular opening 211a formed at a rear end of first casing portion 211 and semicircular opening 212e formed at a front end of second casing portion 212, so that coupling element 26a is secured to casing 210.
Third cylindrical member 27 includes a large diameter section 27a formed at a front end thereof and a flange section 27b formed at a rear end thereof. The large diameter section 27a of third cylindrical member 27 is disposed on an outer surface of the small diameter region 21b of first cylindrical member 21. The large diameter section 27a of third cylindrical member 27 and the small diameter region 21b of first cylindrical member 21 are firmly and releasably attached to each other by, for example, a plurality of screws 27c. Accordingly, first cylindrical member 21 and third cylindrical member 27 are firmly and releasably secured to each other. The flange section 27b extends radially inwardly from a periphery of a rear end of third cylindrical member 27, so that circular opening 27d is defined within flange section 27b. The flange section 27b is arranged to be parallel to a plane perpendicular to the longitudinal axis of third cylindrical member 27.
Thus, the burning mechanism 220 is substantially constructed by first through third cylindrical members 21, 23 and 27, cup-shaped member 25, second fan 34, and fuel supply pipe 26.
The second casing portion 212 includes a rear end plate section 212a formed at a rear end thereof. The rear end plate section 212a is arranged to be parallel to a plane perpendicular to the longitudinal axis of second casing portion 212. The rear end plate section 212a includes a cylindrical region 212b with a diameter designed to be slightly greater than that of third cylindrical member 27. Cylindrical region 212b is arranged, such that a longitudinal axis thereof is located on the longitudinal axis of second casing portion 212. Circular opening 212c with a diameter slightly smaller than that of the opening 27d of third cylindrical member 27 is centrally formed at the rear end plate section 212a. Furthermore, a part of second casing portion 212 adjacent to the rear end plate section 212a is gradually narrowed.
Annular member 28 having a L-shaped cross section is fittingly disposed on an outer surface of a corner 27e which is formed at a time when the flange section 27b is formed. Annular member 28 and third cylindrical member 27 are fixedly attached to each other at their mating surfaces by, for example, spot welding. An inner diameter of annular member 28 is designed to be slightly smaller than that of the circular opening 27d of third cylindrical member 27, but to be slightly greater than that of the circular opening 212c of second casing portion 212.
Annular member 28 is also fittingly disposed on an inner surface of a corner 212d which is formed at a time when the cylindrical region 212b is formed. Accordingly, third cylindrical member 27 is fittingly disposed on the inner surface of the corner 212d of second casing portion 212 through annular member 28.
Fourth cylindrical member 40 is located at a position which is to the rear of third cylindrical member 27. Fourth cylindrical member 40 includes a flange 40a which is formed by bending a front end portion of fourth cylindrical member 40 radially inwardly at right angle. A diameter of fourth cylindrical member 40 is designed to be about equal to that of the cylindrical region 212b of second casing portion 212. An inner diameter of flange 40a of fourth cylindrical member 40 is designed to be slightly greater than that of circular opening 212c of the rear end plate section 212a of second casing portion 212. The flange 40a of fourth cylindrical member 40 is disposed on a rear end surface of the rear end plate section 212a of second casing portion 212. Fourth cylindrical member 40 and second casing portion 212 are fixedly attached to each other at their mating surfaces by, for example, spot welding. When fourth cylindrical member 40 is fixedly attached to second casing portion 212, fourth cylindrical member 40 is arranged such that the longitudinal axis thereof is located on the longitudinal axis of second casing portion 212.
First casing portion 211 includes a front end plate section 211b formed at a front end thereof. The front end plate section 211b is located at a position adjacent to first fan 33 so as to cover first fan 33. Accordingly, an interference between the first fan 33 and objects from outside of the heating apparatus 100 is effectively prevented. Circular opening 211c is centrally formed in the front end plate section 211b of first casing portion 211 so as to provide communication between the outside and the inside of casing 210'.
Heat exchanger 50 includes an outer annular cylindrical member 51 and an inner annular cylindrical member 52 spaced radially inward from the outer annular cylindrical member 51. An outer diameter of the inner annular cylindrical member 52 is designed to be smaller than an inner diameter of the outer annular cylindrical member 51. An axial length of the inner annular cylindrical member 52 is designed to be slightly smaller than that of the outer annular cylindrical member 51. First circular plate member 53 is fixedly disposed at a rear end of the outer annular cylindrical member 51. Second circular plate member 54 is fixedly disposed at a rear end of the inner annular cylindrical member 52. The inner annular cylindrical member 52 includes a plurality of projections 52a which project radially inwardly from an inner peripheral surface of inner annular cylindrical member 52 as illustrated in FIG. 7. A plurality of axial passages 52b are defined between the adjacent projections 52a.
Heat exchanger 50 further includes an annular plate member 55 which bridges between a front end portion of the outer annular cylindrical member 51 and a front end of the inner annular cylindrical member 52. An inner peripheral portion of the annular plate member 55 is fixedly received on a front outer surface of the inner annular cylindrical member 52, and an outer peripheral portion of the annular plate member 55 is fixedly received on an inner surface of the front end portion of the outer annular cylindrical member 51. Thus, annular hollow space 56 is defined by the outer and inner annular cylindrical members 51 and 52 and the annular plate member 55. Furthermore, when annular plate member 55 fixedly bridges between the outer and inner annular cylindrical members 51 and 52, cylindrical hollow space 57 is defined between the first and second circular plate members 53 and 54.
The inner annular cylindrical member 52 of heat exchanger 50 is firmly and releasably secured to the rear end plate section 212a of second casing portion 212 by, for example, a plurality of screws 58. In this securing manner, a shaft portion of screws 58 are engaged with the corresponding female screw portions 52c, which are formed at an inner peripheral surface of the inner annular circular member 52 as illustrated in FIG. 7. When the inner annular cylindrical member 52 is secured to the second casing portion 212, fourth cylindrical member 40 is disposed within an inner hollow space of the inner annular cylindrical member 52 of heat exchanger 50.
Heat exchanger 50 is provided with a heat medium inlet port 60 which is centrally formed at first circular plate member 53, and a heat medium outlet port 70 which is formed at a front portion of the outer annular cylindrical member 51. Combustion gas outlet port 80 is formed at the front portion of the inner annular cylindrical member 52, and penetrates through the outer annular cylindrical member 51. Furthermore, the heat medium outlet port 70 and the combustion gas outlet port 80 are angularly offset from each other by about 180.degree. with respect to the longitudinal axis of heat exchanger 50.
Heating apparatus 100 described above is assembled as follows. First, a sub-assembly "B'" is prepared in a separate subassembling line in accordance with the following sequential steps (a')-(g').
(a') First and second cylindrical members 21 and 23 are temporarily assembled to each other by disposing flange portion 23a of second cylindrical member 23 on second annular planar region 21d of first cylindrical member 21 and maintained so that indents 21f of first cylindrical member 21 are received in the corresponding circular holes 23b of flange portion 23a of second cylindrical member 23.
(b') Fuel supply pipe 26 is secured to flange portion 23a of second cylindrical member 23 by caulking and maintained so that nozzle 26a of fuel supply pipe 26 penetrates through second cylindrical member 23, and the coupling element 26a to which one end of the fuel supply pipe 26 is fixedly connected is received within semicircular cut-out portion 21h which is formed at one peripheral portion of the front end of first cylindrical member 21.
(c') Fan motor 30 is firmly secured to first cylindrical member 21 by screws 22 together with second cylindrical member 23.
(d') First fan 33 is firmly secured to the front end portion of drive shaft 32 of fan motor 30.
(e') Cup-shaped member 25 is firmly mounted about the rear end portion of drive shaft 32 of fan motor 30.
(f') Second fan 34 is firmly secured to the rear end of drive shaft 32 of fan motor 30 by bolt 34a.
(g') First cylindrical member 21 is firmly and releasably secured to third cylindrical member 27 by screws 27c. Thus, the sub-assembly "B'" is prepared.
Now, heating apparatus 100 is assembled in accordance with the following sequential steps (1')-(3').
(1') The rear end plate section 212a of second casing portion 212 is firmly and releasably secured to the front end of the inner annular circular member 52 of heat exchanger 50 by screws 58 and maintained while fourth cylindrical member 40 fixedly connected to the rear end plate section 212a of second casing portion 212 and thus is disposed within the inner hollow space of the inner annular cylindrical member 52 of heat exchanger 50, which has been already assembled.
(2') The sub-assembly "B'" is inserted into second casing portion 212 and maintained while the corner 27e of third cylindrical member 27 is fittingly disposed on the inner surface of the corner 212d of second casing portion 212 through annular member 28.
(3') First and second casing portions 211 and 212 are firmly and releasably connected to each other by screws 240 through the corresponding pair of L-shaped plates 241 and 242 so that an outer surface of large diameter region 21a of first cylindrical member 21 is in fitting contact with an inner surface of second casing portion 212, and the coupling element 26b is fittingly received in semicircular opening 211a of first casing portion 211 and semicircular opening 212e of second casing portion 212.
Thus, a process of assembling the heating apparatus 100 is completed.
Furthermore, when first and second casing portions 211 and 212 are firmly and releasably connected to each other, fan motor 30 is arranged, such that a longitudinal axis of drive shaft 32 of fan motor 30 is located on the longitudinal axis of first casing portion 211.
In operation of heating apparatus 100, air is introduced into chamber 250, which is defined by first casing portion 211 and first cylindrical member 21, from outside of casing 210' through circular opening 211c of the front end plate section 211b of first casing portion 211 by virtue of the rotation of first fan 33. The air introduced into the chamber 250 moves to chamber 260, which is defined by second casing portion 212, first cylindrical member 21 and third cylindrical member 27, through a plurality of holes 21i formed at first annular plane region 21c of first cylindrical member 21. The air in chamber 260 further moves to an inner hollow space of third cylindrical member 27 through a plurality of circular holes 27f formed at a side wall of third cylindrical member 27. The air in the inner hollow space of third cylindrical member 27 is consumed for burning the fuel which is conducted into the inner hollow space of third cylindrical member 27 in a manner described below.
A liquid fuel, such as kerosene in the fuel tank (not shown) is pumped up by a fuel pump (not shown), and is conducted to fuel supply pipe 26 via the external fuel supply pipe (not shown) and coupling element 26b. The fuel conducted to fuel supply pipe 26 is ejected from nozzle 26a, and collides with an inner surface of the side wall 25a of cup-shaped member 25 which is rotating together with the drive shaft 32 of fan motor 30. As a result, a film of fuel having an even thin thickness is formed at the inner surface of the side wall 25a of the cup-shaped member 25. Nozzle 26a is arranged, such that the longitudinal axis of nozzle 26a is situated in a first quadrant of axes "X" and "Y" while the rotational direction of drive shaft 32 of fan motor 30 is clockwise as indicated by arrow "A" in FIG. 3. The even thin film of fuel thus is effectively formed at the inner surface of the side wall of the cup-shaped member 25. The thin film of fuel is gradually moved forwardly, and then is separated from the side wall 25a of the cup-shaped member 25 due the centrifugal force acting on the cup-shaped member 25. When the film of fuel is separated from the cup-shaped member 25, the fuel scatters into a large number of small droplets in the hollow space of third cylindrical member 27. The small droplets of the fuel are sufficiently suspended in the air in the inner hollow space of third cylindrical member 27 by virtue of the rotation of second fan 34. Then, the fuel begins to burn in the inner hollow space of third cylindrical member 27 by virtue of operation of an igniter (not shown).
As indicated by single-dot-dash lines in FIG. 1, the combustion gas produced by burning the fuel moves into an inner hollow space of fourth cylindrical member 40. The combustion gas in the inner hollow space of fourth cylindrical member 40 further moves into the axial passages 52b defined between the adjacent projections 52a of the inner annular cylindrical member 52 of heat exchanger 50, and then moves forwardly.
On the other hand, as indicated by double-dot-dash lines in FIG. 1, the heat medium is conducted into cylindrical hollow space 57, which is defined between the first and second circular plate members 53 and 54, through the heat medium inlet port 60, and moves radially outwardly. Then, the heat medium moves into the annular hollow space 56, which is defined by the outer and inner annular cylindrical members 51 and 52 and the annular plate member 55. The heat medium moved into the annular hollow space 56 then moves forwardly, being guided by a helical groove 52d, which is formed at an outer surface of the inner annular cylindrical member 52, so as to conduct the heat medium helically along the outer surface of the inner annular cylindrical member 52.
When the combustion gas moves through the axial passages 52b forwardly while the heat medium moves through the annular hollow space 56 forwardly, a heat exchange is carried out between the combustion gas and the heat medium through the inner annular cylindrical member 52 so as to heat the heat medium. The heated heat medium at a front end portion of the annular hollow space 56 is conducted to an external heating device (not shown) via the heat medium outlet port 70. At the external heating device, heat of the heat medium is radiated to warm a space in which the heating device is disposed. The combustion gas moved to a front end portion of axial passages 52b moves circumferentially, and is conducted to the outside of the heating apparatus 100 via the combustion gas outlet port 80.
In general, soot is formed at an inner peripheral surface of third cylindrical member 27 due to an unexpected abnormal operation of the burning mechanism 220. The formation of deep soot at the inner peripheral surface of third cylindrical member 27 causes an increase in flow resistance of the combustion gas flowing through third cylindrical member 27, so that a performance of the burning mechanism 220 is decreased. As a result, a performance of the heating apparatus 100 functioning as a heat source of an air conditioning system is also decreased.
Therefore, it is required to remove the soot from the inner peripheral surface of third cylindrical member 27 as occasion demands. In order to carry out removal of soot from third cylindrical member 27, the heating apparatus 100 is partially disassembled in a manner described in below.
A process of partially disassembling the heating apparatus 100 is carried out by performing steps (g'), (2') and (3') in the assembling process of the heat exchanger 100 in reverse. That is, the process of partially disassembling the heating apparatus 100 is carried out in accordance with the following sequential steps (101)-(103).
(101) First casing portion 211 is released from second casing portion 212 after taking screws 240 off from the corresponding pair of L-shaped plates 241 and 242.
(102) The sub-assembly "B'" is taken out from the second casing portion 212.
(103) Third cylindrical member 27 is released from first cylindrical member 21 after taking screws 27c off.
After completion of step (103), removal of the soot from the inner peripheral surface of third cylindrical member 27 is easily carried out because the third cylindrical member 27 is handled separately. Simultaneously, the other component parts of the burning mechanism 220, such as second fan 34 can be checked.
After this treatment, the heating apparatus 100 is reassembled by carrying out steps (101)-(103) in the partial disassembling process of the heat exchanger 100 in reverse. That is, the process of reassembling the heating apparatus 100 is carried out in accordance with the following sequential steps (g') (2') and (3').
(g') First cylindrical member 21 is firmly and releasably secured to third cylindrical member 27 by screws 27c.
(2') The sub-assembly "B'" is inserted into second casing portion 212 and maintained while the corner 27e of third cylindrical member 27 is fittingly disposed on the inner surface of the corner 212d of second casing portion 212 through annular member 28.
(3') First and second casing portions 211 and 212 are firmly and releasably connected to each other by screws 240 through the corresponding pair of L-shaped plates 241 and 242 so that the outer surface of large diameter region 21a of first cylindrical member 21 is in fitting contact with the inner surface of second casing portion 212, and the coupling element 26b is fittingly received in semicircular opening 211a of first casing portion 211 and semicircular opening 212e of second casing portion 212.
In the above-mentioned conventional heating apparatus 100, the following disadvantages may occur. First, since casing 210' of burner 200' is formed by two separate portions 211 and 212 having about the same dimensions, strain caused by forces acting on the casing 210' is concentrated upon a location at which the first and second casing portions 211 and 212 are connected to each other. Accordingly, when the heating apparatus 100 is used in a situation where heating apparatus 100 frequently receives periodic vibrations, for example, when the heating apparatus 100 is used for a heat source of an automotive air conditioning system, and is required to be installed in an automobile engine compartment, the frequent periodical vibrations propagating from the automobile engine compartment cause the concentrated strain on the casing 210' at the location at which the first and second casing portions 211 and 212 are connected to each other. Therefore, over the course of time, the connection between the first and second casing portions 211 and 212 may be loosened so that defective gaps may be created between the rear end region of first casing portion 211 and the front end region of second casing portion 212. Accordingly, if fuel defectively leaks from the burning mechanism 220 in an ignition stage, the leaked fuel from the burning mechanism 220 may be further leaked to outside of the heating apparatus 100 through the above-mentioned defective gaps.
Secondly, when the heating apparatus 100 is reassembled after the completion of maintenance of the burning mechanism 220, the nozzle 26a of fuel supply pipe 26 may not be properly rearranged. Specifically, during a process of reassembling the heating apparatus 100, it is required to adjust a circumferential position of first cylindrical member 21 relative to the second casing portion 212. According to this adjustment, a circumferential position of the coupling element 26b, which is received within semicircular cut-out portion 21h of first cylindrical member 21, relative to the semicircular opening 212e of second casing portion 212 is also adjusted. This adjusting manner causes an unnecessary circumferential movement of connecting member 26b together with the other end of fuel supply pipe 26 opposite to nozzle 26a. As a result, when the process of reassembling the heating apparatus 100 is completed, nozzle 26a of the fuel supply pipe 26 may be erroneously situated in a second or fourth quadrant of axes "X" and "Y" while the rotational direction of drive shaft 32 of fan motor 30 is clockwise as indicated by arrow "A" in FIG. 3. This improper situation of nozzle 26a of the fuel supply pipe 26 causes defective film formation of the fuel along the inner surface of the side wall 25a of cup-shaped member 25, such as a formation of the fuel film having uneven thickness. Accordingly, the fuel may not be effectively burnt in the inner hollow space of third cylindrical member 27, so that the performance of the heating apparatus 100 functioning as the heat source of an air conditioning system is decreased.
Lastly, because that the helical groove 52d insufficiently guides the heat medium, the heat medium flows from the heat medium inlet port 60 to the heat medium outlet port 70 via various flow paths having various distances. The distance of the heat medium flow path from the inlet port 60 to the outlet port 70 varies between the maximum and minimum values which are defined below.
The minimum distance of the heat medium flow path is measured when the heat medium flows through cylindrical hollow space 57 upwardly and then flows through the annular hollow space 56 forwardly to the outlet port 70. On the other hand, the maximum distance of the heat medium flow path is measured when the heat medium flows through cylindrical hollow space 57 downwardly and then flows through the annular hollow space 56 forwardly, and finally flows circumferentially around a front end portion of annular hollow space 56 to the outlet port 70.
Accordingly, when the heat medium flows from the inlet port 60 to the outlet port 70, the heat medium flow paths having various flow resistances are created. The minimum flow resistance is generated when the heat medium flows along the path having the minimum distance, and the maximum flow resistance is generated when the heat medium flows along the path having the maximum distance. As a result, when the heat medium flows through cylindrical hollow space 57 and annular hollow space 56, an uneven distribution of flow rate of the heat medium is generated. Therefore, the heat exchange between the heat medium and the combustion gas through the inner annular cylindrical member 52 is not effectively carried out, so that the performance of the heating apparatus 100 functioning as the heat source of the air conditioning system is decreased.